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Can an F-16 perform Pugachev's Cobra?
I know that the F-16 VISTA tech demonstrator incorporated 2D thrust vectoring and could perform this maneuver. I also know that military variants of the F-16 are prevented from intentionally entering such extreme angles of attack via their flight limiters.
However, I also know one more thing; there is a switch just in front of the throttle that allows "manual pitch override". This disables the pitch-plane limiter of the FLCC to allow the pilot to recover from certain types of deep stalls when normally the flight limiters would freeze the control surfaces due to the detected extreme AOA.
The question is, can U.S. military-variant F-16s, with MPO enabled, perform a "Cobra" maneuver like Pugachev's Cobra?

See Wikipedia's list of aircraft capable of this manoeuvre

No.
This would require a docile pitch behavior of the airframe up to approx. 110° angle of attack. The design of both the Su-27 and the MiG-29 is based on a geometry that has been carefully optimized by TsAGI to behave nicely over its full AoA range, a care that has not been spent by General Dynamics while designing the F-16. The specifications did not call for it, because the idea was to create a low-cost lightweight fighter to complement the heavy F-15.
However, even the F-15 is AoA limited because less care was spent on its aerodynamic refinement. At higher angles of attack, both the F-16 and the F-15 show a nasty pitch-up which cannot be controlled with the aerodynamic control surfaces - only thrust vectoring can manage this. Contrast this which the Su-27, which shows balanced and slightly negative (nose down) pitch moments over the full AoA range, so the limited control authority coupled with the aircraft's dynamics can make the Cobra maneuver possible.

What about the F-35?

@Firee: I do not know the pitch over AoA behavior of the F-35 but don't see how it can be stable with its planform. Stealth was more important than aerodynamics, and to be honest, the F-35 is a dog in comparison to the F-16 (at least the earlier models, before they were burdened with all that added equipment for multi-role capabilities).

@Firee The F-35 is docile in pitch up to 50°. This is already much better than the F-16, but not enough for the Cobra maneuver (which is only good for airshows anyway).

I don't quite understand why the Soviet is so obsessed the nose down stability thing. That alone delayed Su-27 development for 1-2 years.

@user3528438 Poor experience with the MiG-23 was the reason. Maybe they overcompensated, but funds for military development were almost unlimited and if the next specification called for a certain goal, they made sure it was met.

I wouldn't call a maximum nose-up pitching moment close to 0.4 as 'docile'. Using the TsAGI Su-27 Cm curve as a reference, the Su-27 has a negative static margin (unstable) until 25° α, and a positive Cm until 70° α, where pitch-rate reaches its maximum. Above 70° α, Cm become negative and pitch-rate reduces to 0 at 110° α. The F-16 exhibits the same negative static margin but a positive Cm only up to 65° α. The F-15 however only has a positive static margin.

It's a no - simply because of the AoA limiter.
Basically the MPO switch is only for getting out of a Deep Stall condition (the switch was added around Block 5).
For the F-16MATV program they removed the AoA limiter and tested it (including A-A) in the early 90s. It could do all the high Alpha stuff the YF-22 could do simple as really.
So yes it was Multi Axis Thrust Vectoring (MATV) not 2D - it had to be - the TV is basically providing the Yaw directional stability the tail cannot provide at high Alpha (not unique affects most single tail jets).
TV was going to be fitted to the entire fleet - the MATV had a GE engine but P&W had also started on one - but they decided it wasn't required.

In reality no. But in theory if no FLCS is present, according to the pitching moment coefficient (Cm) curve, then yes.
Please refer to the Cm curve from the NASA F-16 wind tunnel data in NASA TP-1538.

The nose-up moment (Cm > 0) below 65 deg AOA, typical to a relaxed static stability fighter aircraft, can provide considerable pitch rate. Owing to the kinetic energy of rotation, the attainable angles of attack exceeds the trim angles of attack (Cm = 0). The higher pitch rate by the nose-up moment, the greater is the dynamically attainable max angle of attack. Then the nose-down moment above 65 deg AOA enables the pitch motion to be stopped naturally.
Likewisely, the Cm curve of Su-27, F-18, Jas-39 and aft cg F-35B.
Su-27, by TsAGI at AIAA-1993:

F-18C:

Jas-39 by SAAB official document:

F-35B by AIAA-2019:

There's also a plot of F-15 Cm-CL chart, but as noted it's not a Cm-alpha chart. As you can see the F-15 is statically stable in a ranges of CL.

Very good answer. But remember that static stability is related to the slope $dC_m/ d\alpha$ and not to $C_m$ itself. Relaxed static stability can therefore be seen in that plot only for $\alpha <25°$ (at least for the upper plot).

@sophit, yes, as I illustrated the slope (static margin) in the F-18 Cm curve. (Because its x-y axis is altered compared to other graphs.) But well, the pitch rate is accumulated according to the integral component of Cm > 0.

No, due, primarily, to the fact that the "cobra" maneuver is entirely useless in ACM/BFM. There is no need for the flight software to support such a maneuver.
Any fighter pilot who left himself in a zero energy state after a purely defensive maneuver like the so-called "cobra" will find himself with a much-deserved missile up his tailpipe.
Pugachev's Cobra is an airshow maneuver, nothing more.

Please note, that I agree 100% on your reasoning and assessment, however no where in the question is it stated "for combat." P's cobra may very well be an airshow and "in the movies only" type of maneuver, but the question is simply asking if the F16 can do it. And yes, I did +1 you.


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What would prohibit a T-38 Talon from being certified in the Acrobatic category?
The definition of the acrobatic category in FAR 23.3 reads as follows:

(c) The acrobatic category is limited to airplanes that have a seating configuration, excluding pilot seats, of nine or less, a maximum certificated takeoff weight of 12,500 pounds or less, and intended for use without restrictions, other than those shown to be necessary as a result of required flight tests.

Considering that the Northrop T-38 is a two-seat, twin-engined supersonic jet trainer aircraft with a USAF service maximum takeoff weight of 12,093 lbs (from their factsheet), what traits of the T-38 would have prohibited Northrop from applying for a civil Type Certificate for the T-38 in the acrobatic category?

What is a civil type certificate.

@Ethan It is basically a certificate issued by the regulatory authorities signifying the airworthiness of an aircraft design. i.e. it signifies that the particular aircraft design is safe to operate subject to conditions in the certificate.

A type certificate - civil or otherwise - costs a lot of money to obtain. Once obtained there are costs associated with maintaining it. If the potential market is not big enough to sustain these costs, there is no business case to seek the certification.

That an aircraft is eligible for a category is not a basis to say that the aircraft should be certified in that category. In other words, though there is nothing prohibiting T-38 being certified in acrobatics category, FAA will not certify it unless someone approaches it for that reason.
The T-38 would come under military surplus aircraft, which is covered by FAA Advisory Circular 20-169 for Military and Special Mission Modifications and Equipment for Commercial Derivative Aircraft.
However, there are some T-38s being operated by civilians in US, which are type certified under FAA Experimental Category (most are used by NASA, Boeing etc for research). One of the aircraft owned by Thornton Corp. is certified under the 'Exhibition' category, which permits the user,

to exhibit an aircraft’s flight capabilities, performance, or unusual characteristics for air shows, motion pictures, television, and similar productions, and for the maintenance of exhibition flight proficiency.

I'm not sure if this aircraft has been used in that manner though.

F-5 (Fighter version of the T-38) were used as stand in for russian MiG's in the Top Gun movie, I don't now if that counts.

@Essah, those F-5s were (maybe still are) used for Dissimilar Air Combat Training, but they were operated by the US Navy, not by a civilian operator thus not requiring a Type Certificate.

The short answer is the FAA has recently moved to a flight test basis for certification of civilian aerobatic aircraft.
The average human body can withstand (https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2091-61.pdf) +4-5G's before loosing consciousness. To be certified for acrobatic maneuvers The FAA had previously required an aircraft be certified for at least +6 and -3g.
However, according to https://www.faa.gov/regulations_policies/rulemaking/recently_published/media/Part23_FinalRule_2120-AK65_WebCopy.pdf,
"For the reasons explained in the NPRM, the FAA removed the acrobatic category
from part 23. The FAA agrees with Velica that the limitations for an airplane certified for aerobatics should be based on flight tests, but believes more specificity is warranted. Therefore, the FAA will require airplanes certified for aerobatics to comply with the limitations established under subpart G of part 23 in this rule."
As already stated, military planes do not have to comply with Federal Law but the Govt does attempt to comply when reasonable (or cost effective) to do so. Interestingly, a YouTube Video (I was unable to find the link) documenting the Airforce F16 Thunderbird's said the F16 engines had to be extensively modified for aerobatic show performance. In other words, military aircraft are normally designed for only a few seconds of inverted flight.
So the FAA is now using a flight test basis for certification of civilian aerobatic aircraft.

"The average human body can withstand +4-5G's before loosing consciousness."  That figure can be dramatically increased with proper physical conditioning, awareness, and anti-GLOC techniques.

But only for a few seconds.

Depends on your definition of a few.  Have you been through military centrifuge training?

According to this military training study, <a href=https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=25&cad=rja&uact=8&ved=2ahUKEwjNp9Xgq9vgAhVCj1QKHU6wA6QQFjAYegQIAhAC&url=https%3A%2F%2Fapps.dtic.mil%2Fdtic%2Ftr%2Ffulltext%2Fu2%2Fa196171.pdf&usg=AOvVaw2eiox6FiopqU_HaHodKBL3>study most military pilots began gray out at 5g@5s or 4g@10sec to be "g" rated they must do 9g@10sec and 40% washed out!

I can't dispute the results of their study, but I am a retired military pilot and I have been through centrifuge training. With some basic training on G awareness and training on techniques to mitigate the effects a pretty average pilot is fully capable of sustaining 4-5 Gs for far, far longer than that. A little bit of tunnel vision or "grey out" is not at all the same thing as losing consciousness.

Only 2.4% of 741 students (approx 1 in 300) getting the high G-training did not get G-LOC at 9g@15sec.

What is your point?  I'm not arguing about a high fallout rate at 9 Gs, I am saying that 4 to 5 Gs isn't a very big deal if you are trained.

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What is this trio of fins at the back of a T-38?
On a T-38 Talon on static display at a museum, I spotted a trio of aerodynamically shaped devices located aft of the vertical tail and between the engine aftbodies fore of the nozzles, as shown in the photos.  If these are vortex generators (VGs), what in the world are they doing there where there's no aerodynamic surface aft of them for the energized vortices to flow over? Could they be some other sort of protuberance, such as antennae for some system on the aircraft?

Can you tell us what museum? I've looked through Google images of T-38 tails and none that I've seen have the same "fins" on the back. It would help to know what variant of the T-38 you are photographing, maybe even a tail number.

@RonBeyer -- this particular specimen is chilling out at the South Dakota Air and Space Museum near Ellsworth AFB -- sadly, I don't have the variant or tail number handy.

I just checked USAF Tail number 23645 at the Frontiers of Flight Museum in Dallas, TX. It does not have those protrusions. The best course of action would be to ask the museum what the last role the aircraft was used for was. That will lead to the answer of who added those components and why.

The aircraft in question is 58-1192 (picture), an YT-38A, which is one of the first prototypes of the T-38.

@Jordy The second prototype, to be precise, if this source is to be believed...

There doesn't have to be any aerodynamic surfaces for it to act on, but there is something else that may benefit from having vortices created there - the end of the aircraft.  The drag created from the bound airflow coming off the fuselage and lower tailplane at that point may be reduced by disturbing the airflow at the point where the drag increases - in this case, where the aircraft ends.

@Moo -- good point, although what did they do about said tip-of-tail drag rise in the production models?

@UnrecognizedFallingObject they may have changed something further forward on the fuselage, which changed the airflow over that part of the aircraft, reducing the need for the vortex generators, or any number of things :)

My car has small protrusions around some of the windows that creates a disturbance to prevent low-frequency oscillations when the windows are cracked or open. The sun roof has a particularly interesting 'comb' that pops up. You can actually pull it down with your fingers and experience the weird pressure oscillation it prevents! Since this is right next to a very un-streamlined feature on the fuselage, I can imagine it serves some similar purpose.

There are a couple of possibilities, both out of the T-38 Flight Operations Manual.
It's a nozzle for a smoke generator.  This was an option on the T-38 airplane to generate a smoke trail behind the aircraft for training purposes.
If possible, inquire if that aircraft was an AT-38B.  Those aircraft apparently had an optional 'ballast box' in that region, which I'm assuming was some sort of a counterweight placed there in conjunction with the bomb racks for practice bombs and other range equipment.
As to the vortex generators?  Who knows!

Hi Carlo, I agree they probably have to do with smoke. I would guess the opening below the three vanes is for smoke, and the three VGs keep the separated flow between the engine nozzles down so the smoke trail stays more coherent. Just a guess, though.

Several of the aircraft I have worked on have vortex generators just a head of the fuel dump area, especially if they're near the exhaust. Those do appear to be right about the fuel dump on that aircraft.

Interesting -- did the T-38 ever have support for dumping fuel though?

I believe the fuel dump vent was on the vertical fin right above the rudder on a T-38.

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What kind of delay does the A320's fly-by-wire system add?
More precisely, I am wondering if there is any kind of data on how long it takes between moving the sidestick and observing a reaction on the ailerons or elevator. I know that the physical control surfaces take time to move and, thus, I am only wondering about the actual latency added by the fly-by-wire (FBW) system.
My naive assumption is that the A320 runs a fixed control loop with precise timings. So, every $n$ milliseconds it samples the sidestick, calculates the necessary control surface deflections and then sends that via some bus which runs at $m$ Hertz. So, on average there is an expected delay of $x$ milliseconds between input and the control surfaces starting to respond to the input.
Also, is the delay noticeable by pilots?

@mins That comparison is irrelevant: there is a lot more between mouse and screen than just the display refresh rate!

Note that human reaction times are of the order of 100ms.  While not directly what we need here (and hence not an answer) it's indicative.  In a completely different field (aligning lasers) a 10Hz feedback rate feels like things are happening with no delay, slightly slower and it really doesn't feel like a realtime response.

@kebs: It is relevant, I'm not talking about the monitor refresh rate, but the GUI refresh rate (rendering rate).

Normal controls should have delay as well if you apply the speed of light theory :)

@mins as a gamer I can definitely state that there is a clear, noticeable difference between 30hz and 60hz.  Friends with 120hz monitors say that step is almost as noticeable.

Controlling an RC helicopter is much, much more twitchy and much more dangerous (yes, people have died from RC helicopters - including a top pro pilot who managed to decapitate himself) thane either gaming or flying real airplanes. Controlling RC helicopters require much faster reflex and reaction times. However, RC equipment has a fixed 25Hz refresh rate (add to that the few milliseconds of CPU processing lag on the transmitter, receiver and servos). 25Hz is fast enough for humans to control an aircraft and feel real-time

It should be noted that RC pilots can feel lag but only if they fly two different control systems - for example testing a different brand's radio or changing servos to different brands. If you only fly the equipment you're used to flying it's nearly impossible to tell that there's any lag

Well, that is complete bull just like this: https://arstechnica.com/staff/2015/02/to-the-audiophile-this-10000-ethernet-cable-apparently-makes-sense/ frame rate on monitors is partly about smoothness, so it's still a positive if there is no other benefit.  A slower frame refresh adds to the input lag of the monitor on the whole, which can easilly be multiple frames if it's a TV being used for example.  So it's 2-sided.  The total input lag, and being able to see inconsistencies in the smoothness of the image as it changes.

Yes there will be a delay, but the delay caused by the control loop is really tiny. I've seen position control loops run successfully and stable at a couple of hundred Hz for simulator motion systems, and the time delay is just one iteration frame = less than 10 msec.
And as @ymb1 correctly points out, if we deflect any control surface the end position is subject to actuation forces, aerodynamic pushback forces, inertia of the surface, cable stretch and -friction, aero damping, maximum flow velocity through the servo valve etc etc. The total transfer function of stick input => surface position is such that an extra time delay of 10 msec in the total loop is not really noticeable. And control position is only the input of the aircraft response, with aircraft inertia playing a large role.
So my answer would be: a tiny time delay that can be totally disregarded.

Are the control input positions really polled sequentially by a loop or are preemptive interrupts used instead?

@mins Most industrial control systems run on PLCs and PLCs, at the very bottom, run a loop.  Conceptually, and for most practical purposes, they are programmed as, and model, a massively parallel state machine, but the state itself, by nature of the limitations of the underlying hardware, is discretized into time slices of duration required to fully evaluate the state of the system (ie: the "scan time", "frame time", or loop time).  One loop consists of reading inputs, evaluating the control logic, and updating the outputs.

@mins That said, for extreme circumstances most such control systems do allow for interrupts to initiate an immediate read of an input (or write to an output) during logic evaluation (ie: outside the loop) but this can actually break the otherwise guaranteed and regular maximum scan time and introduce more side-effects than it's usually worth.  Typically when one is tempted to resort to such an interrupt it's a sign that the control system needs to be subdivided instead, with the more time-critical subsystem given its own controller (and that's what's usually done).

@J... Thanks for the clear explanation. I discovered PLC. Wikipedia also emphasizes the time predictability of the processing.

@mins To be clear, a flight computer is completely specialized, of course, and won't work exactly like an industrial PLC, but any "digital fly-by-wire" systems will have something like this at the bare-metal layer.

@J... Hmmm... I'm not so sure. I'd be a little surprised if they used PLCs rather than CPUs running an RTOS (or bare-metal application.) They would almost certainly use a control loop in any case, though.

The A320 uses late 80s era microprocessors for the control loops, Motorola 68020 and similar.

@reirab Yeah, absolutely.  I mean, a PLC was just an example - like I said, a flight computer is completely bespoke.  It's still the same type of discrete, loop based state machine running on a thin RTOS with an ancient CPU.  Flight computers are probably based on something closer to OS9 and massively multithreaded, albeit to similar ends (a PLC is actually effectively a single-threaded process whereas an RTOS type of system lets you have something like many independent PLCs in one box).  A PLC is just a nice and simple device to demonstrate the concept.

@reirab: Actually the PLC comparison is quite apt. He basically described how servos work. You can think of digital servos as special-purpose PLC's running a PID loop (LITERALLY a PID loop - the core of PLC programming). Of course the programming is fixed so they're not program in ladder logic but more often than not assembly.

@slebetman Right. I just meant that they generally use regular CPUs, not programmable logic devices. The algorithms (e.g. for envelope protection) would probably be too complicated for programmable logic to be the most reasonable solution. Not that you couldn't do it (e.g. with an FPGA,) just that a CPU running a real-time control loop would make more sense.

The overall control response of a fly-by-wire might be even faster than mechanical because 1) it avoid any flexing in the mechanical or hydraulic transmission (the actuators are still hydraulic, but the electrically-controlled valve is at the actuator, so the pressure does not have to spread far) and 2) the computer can boost the initial deflection to overcome inertia and then reduce it back a bit and can add a brief counter-command when the controls are neutralized.

From practical experience working with these kind of systems, I do not think that the delay is as low as 10ms. I would expect more in the neighbourhood of 100ms, which would still be totally acceptable (and not noticable for the pilot) for the given purpose.

I don't have an answer for the timings (I personally don't think that's publicly available information), but I can answer this

is the delay noticeable by pilots?

as I have some direct experience, and I can affirm that no, the pilot does not perceive a delay between a stick deflection and the aircraft reaction.

I'd assume that the delay is approximately that of the power-steering you get in most cars.  To give people a comparison to something they may have experience with.

@Baldrickk you train so much and so long, that by the time you have to actually pilot, you don't need to compare it to driving anything else.

not everyone reading this will be a pilot ;)

@Baldrickk ah, I thought that by "people" in your first comment you were referring to "those who pilots", not readers here, sorry.

No, no, you can move a side stick much,  much more quickly than moving the conventional controls.
Side stick inputs to the computers are updated every 10 ms which is extremely fast, this corresponds to 100hz update;  compared to most television pictures update, FBW is twice as fast.
for very small displacement of conventional flight control, you have no flight control effect because of the system Backlash
For very fast and large inputs in FBW, the order is voluntarily dampened to protect the aircraft structure, in conventional flight controls there is no protection, you may damage the structure, mainly when the rudder is concerned even though the range is mechanically limited while in full FBW RUDDER, pedals EFFECT is voluntarily dampened when it gets dangerous to the structure
As a summary no ADDITIONAL delay with FBW


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Why do some air forces not allow color-blind pilots?
Some air forces, e.g., the Indian Air Force (IAF), do not allow color-blind pilots. Is this local only to the IAF or a global procedure?
Also, are there any regulations regarding commercial pilots not being color-blind?

For commercial pilots it is important that they can distinguish the red, green and white light signals as described in http://aviation.stackexchange.com/q/5143/524.

It's important to remember that color blindness is not always a you are or you're not condition but rather a matter of degree. For example, I was able to pass the color requirement for a 3rd class medical, but when I wanted a 2nd class medical, I couldn't. However, they gave me a waiver based on shining light signals at me from a tower when I was on the ground. When I wanted a 1st class medical, I had to see the light signals from the air. Some years ago, they lessened the requirements considerably, and I found I could pass the 1st class color requirement and no longer needed a waiver.

Why would any Air Force allow color blind pilots sounds like a better question to me. Honestly, it seems pretty questionable to me for someone who is red-green color blind to even be issued a pilot certificate.

@reirab The term "colour-blindness" is unhelpful, since "blindness" suggests an absolute. Like anything, it's a matter of degree.

@Terry you might consider rolling that into an entire answer for the second of the two questions posed by the OP...

In fact, most militaries don't take colorblind people into flight school.
Colorblindness can be a serious problem for a pilot, because in the interest of cost and/or simplicity, not all indicators in an aircraft cockpit are colorblind-accessible. It's really cheap to use a two-way red/green LED as a status indicator (and by quickly alternating the current through the LED you get amber); it's much more expensive in electro-mechanical systems to combine text and color so that the status can be deciphered by someone who is red-green colorblind. It becomes easier again in a glass cockpit, but that increases cost and there are still concerns like screen resolution to consider when designing text-and-color displays. While it's in the general interest of aviation manufacturers to design certain avionics with as many overlapping visual cues as possible, it's not always feasible to specifically design towards colorblind accessibility in every circumstance.
Here is a set of spectra simulating how various forms of colorblindness would change a person's perception of the normal color set:

Protanopia and deuteranopia are various forms of red-green colorblindness, the most common form of dichromia (protanopia is a deficiency in red cells, deuteranopia a deficiency in green; the results are similar because red and green are close in wavelength). Tritanopia is commonly called blue-yellow colorblindness and is less common, with full colorblindness (monochromia) being very rare.
From this chart, we can deduce the following basic difficulties for a red-green colorblind person attempting to operate a plane:

Red on brown, or any dark color, would have no contrast. That would make reading (and setting) this Cessna radio stack nearly impossible:

... as well as decreasing the contrast of red lines on high-elevation sectionals (like Charlie/Echo space boundaries, non-towered airports, NDB frequencies etc):

Green and yellow are practically indistinguishable. That would make discerning the borders of inhabited low-lying areas on sectionals difficult:

... as well as making the color-coding of this airspeed gauge much less useful at a glance:

Blue and magenta are indistinguishable, as are cyan and white. That makes your GPS useless over water; where's the magenta line?

While you could probably get around most of these difficulties (buy a nav stack with blue LED displays, trace the borders of your sectional charts in something, configure the GPS to give you a white line, etc etc) these are all images that people with full color vision would be able to discern at a glance, which in an emergency situation is often a life-or-death advantage.
That point is especially true for military pilots, who are typically subject to more rigorous medical screening and training including very high requirements for visual acuity (often better than 20/20 uncorrected vision). If you can't see extremely well in a combat situation, you will either fail to spot an enemy until he has gained a significant advantage over you, or you will fire on friendly forces; either way, you're a liability. Coupled with the fact that everyone and their brother grew up dreaming of being a fighter pilot, flight schools get to be picky. Therefore, military aircraft cockpits are typically designed with the assumption of full color spectrum perception, because the only people who will ever be in them will be able to tell red from green, blue from yellow.
Consider, just as one example, a hypothetical conflict in the Middle East involving the Turks and Iranians, where NATO and thus the USAF is also involved. Both of these countries still operate variants of the F-4 Phantom. With an ROE requiring visual confirmation of a hostile, if you are in a USAF F-22, in a visual-range tangle with an F-4 whose IFF is inconclusive (either non-functioning or malfunctioning) and you can't tell the difference between these two rondels...

... you are screwed. The fact the Phantom is maneuvering against you is what any pilot would do when approached by an aggressor aircraft; a Turkish pilot isn't just going to sit there and be shot down by friendly fire, he'll engage defensive, so you can either shoot and risk spending the rest of your life in Leavenworth for dereliction of duty, or break engagement, presenting your tailpipe to the other craft and hoping it's not hostile. Fifty-fifty shot either way with a hundred and fifty million dollar plane on the line, not to mention your life. Your first clue it's an Iranian would be a missile launch, and no matter how much more advanced USAF craft are now than in the era of the F-4, an aircraft that has successfully launched a short-range missile at you has you by the wrinkly ones.
In addition, ground lighting systems are often not differentiable either. For instance, there is an important difference between a heliport beacon flashing green-yellow-white versus white-green-red (the one including a red flash is a hospital helipad and off-limits to gen-av traffic even in an emergency), but a red-green colorblind person may well not be able to tell the difference. Runway end lights are either green or red, indicating traffic direction (though there's usually a secondary cue of the approach array lights sequencing toward or away from the runway edge). Similarly, to a person for whom red is indistinguishable from white, the red-over-white glide slope indicator at the end of the runway would be useless (this would typically happen only with full colorblindness). Blue-yellow colorblindness is the other major type of partial colorblindness, and it would cause other problems like decreasing readability of navigation charts (for instance, incorporated land areas are yellow on FAA sectionals, while Victor routes and class B/D airspace borders are different blues) and trouble negotiating taxiways as the blue taxiway lights would look the same as yellow-white indicator lights elsewhere on the tarmac.

There are also no radio communication procedures (lights from the tower) that would be impacted.

This answer would be "even better (tm)" if you included pictures of the items that you discuss in the last paragraph (papi, charts, tower lights, etc.)

But why make the LEDs red/green? I get its too costly for full multi-color LEDs. But couldn't they have used a different 2-color combo like blue/yellow? While that would still be exclusionary, it would exclude far less people. Or couldn't you have indicators via location? The guage could just have markers and labels instead of colors. I'm sure there are plenty of other accessible fixes that wouldn't drastically increase cost.
The only thing I see as an issue at all is with identifying allies vs enemies, but I feel like that could also be handled, I just don't know how

@Merlin-they-them- The answer to that is a history of the development of the LED and other light-emitting displays. The shortened version is that we've had green CRTs since the 50s, and red (and then green) LEDs since the late 60s. Producing bright blue light from a diode presented very basic physics problems that weren't solved until the late 90s, and the technology didn't proliferate until the 2010s. Up until then, your choices for LED indicators were red, green, and (by combining them) amber.

While the late 90s were nearly 25 years ago, a large portion of the airframes in current US service (military or civilian) are much older than that; yes, they get upgrades, but on nowhere near the lifecycle of consumer electronics, because these systems have to have universal acceptance. A combination of glacial government regulatory movement to require new systems, and the "principle of least astonishment" being a major life safety concern in aviation, means that what pilots consider "standard equipment" evolves very slowly.

In the United States, military pilots must have full color vision. We have something like 100 applicants for every 1 position, so there is no question of accepting pilots who have vision problems. Military pilots are expected to have flawless vision.
Vision, including color vision, is very important for all pilots, not just military pilots. Flying requires picking out tiny lights of different colors from long distances away. I remember the first time I did night flying, boy was that hard. You would fly towards a city with literally millions of lights surrounded by complete blackness and the instructor would say, "Where's the airport?" You have to visually pick out a tiny little white and green light from a long distance away out of millions of other lights. Red and green lights are very common. For example, the nav lights on aircraft are red and green. If you could not tell the difference, you might not be able to tell if another aircraft is coming towards you or moving away from you. There would be many other problems as well.

You also wouldn't be able to tell which of you has the right-of-way (i.e. are you seeing the left wingtip or the right wingtip of the other airplane?)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Why are pilots deemed unfit to fly after emergency ejection?
There are many instances where pilots need to eject out of the cockpit due to emergency situations, and after such an ejection from some modern aircraft, pilots are deemed unfit to fly airplanes for some years. Why is this done? What is the minimum number of years after which a pilot is deemed fit to fly again?

Depends on the aircraft.  Canadian F-18 pilots are allowed to eject once, I believe.  After two they are no longer allowed to fly (afaik) - damage to the spine, as noted by @MikeFoxtrot, is the primary reason.

thanx @BobJarvis

Captain Udell ejected supersonically and my understanding is that he was still able to fly again after his ejection.  http://jalopnik.com/5894022/what-happens-when-you-eject-out-of-a-jet-at-800-mph

Air force pilots often fly aircraft worth millions, or billions, of dollars. I suspect that the automatic suspension gives them one more reason to stay in the aircraft.

@Hal, I can tell you that the price of the aircraft is not part of the pilot's decision making process when facing a life or death situation.

Ejection Seats are not a free ticket out. They are incredibly violent and rough on your body. This newspaper article has a more chilling quote from an interview:

About one in three will get a spinal facture, due to the force when the seat is ejected - the gravitational force is 14 to 16 times normal gravity and it might be applied at 200G per second. Bruising and abrasions are typical from the shock of the chute opening or the air blast. In the early days, there were cases where pilots would eject into very-high-speed air and it would whip their arms behind and break them, pop their shoulders out; same thing could happen to the legs. Source

Hence, it is very possible to get back pains and a host of other problems as a result of ejecting. Since these type of things are not that easily reversible, you'd rather take the safe path and remove then from the cockpit than put then back in a work environment that known is pretty hard on your body. Aircrew seem to agree:

“It was the most violent thing I’ve ever felt in my life,” says one of the B-1 crew members, whom the Air Force asked me to identify as “Captain IROC.” “I lost a full inch in height,” because his spine absorbed such tremendous G-forces. Source

Modern ejection seats are however increasingly intelligent and will gauge the ejection force applied to the conditions, cutting down the number of serious cases.
This paper discusses the symptoms of four individuals who crashed their jets in mid-air. The medical problems encountered with ejection can be classified as follows:

Injuries from the emergency that causes ejection—fire or collision.
Canopy jettison: burns from “MDC splatter” and cuts from fragmented plastic. For these reasons, aircrew are always advised to wear their visors down, to protect the face.
Firing of ejection gun: spinal injuries.
Entering airflow: wind blast may cause lung damage; seat tumbles at variable speed, which may be as high as 180 rpm. (All seats have a drogue parachute or deployable aerodynamic panels to prevent tumbling); flail injuries to extremities.
Parachute deployment: snatch injuries.
Landing: lower limb injuries.

I have read anecdotal stories of pilots measuring a full inch shorter following an injection owing to compression of the disc in their spines. Ejection is bascially like being shot out of cannon. Somehow, you usually see slow motion films of ejection but if you see a real-time eject, it's just "bang" and the pilots not in the cockpit anymore.

Common initial ejection forces can be in excess of 500G's with the sustained G rates that you cited, roughly 12-16,  all dependent on aircrew weight.  The vast majority of injuries occur at initial ejection and entrance into the wind stream.  High speeds ejections cause massive flail injuries and basically windmill your arms and legs.  Otherwise, most ejections result in major damage to lower extremities because you hit the ground at roughly 25-30kts.  Ejection seats have evolved enough that spinal injuries seem to be less concerning than the were years ago.

For completeness sake, in a single-seat aircraft you're looking at about a 0.4 sec exit time with a parachute deployment starting at between 1-2 secs.  That alone is insanity.

The ACES-II ejection seat (marketing tagline: "Thrust You Can Trust") in the F-16 completely removes the canopy from the aircraft before the solid rocket motor (!!!) ejects the pilot from the aircraft.  It's capable of removing a pilot from a stationary aircraft and lofting them to enough altitude that the parachute can fully deploy.  It's designed so that both hands are between your legs when you pull the ejection handle, trying to mitigate the "flailing" injuries at high speeds.  Still, I must agree with the author, it is EXTREMELY violent and injurious.  Beats the alternative.  Not by much.

@Meower68 You're not holding onto anything at 500kts.

Do you happen to know what fraction of pilots who eject suffer no significant or lasting injuries?

@Mehrdad That sounds like a decent separate question.

love the "newspaper science" there "200G per second"  :)

@JoeBlow G is a measure of acceleration.  G/second is a measure of the rate of change of acceleration.  The rate of change of acceleration is sometimes called "jerk."

TIL: I have been deemed the rate of change of acceleration.

I don't know anything about minimum periods - but that may depend on the air force in question.  (Maybe someone else knows.)
Medical complications can arise years after an ejection.  A fairly well known case I've heard about is the astronaut Michael Collins, who ejected from an aircraft in the 1950s.  More than ten years later he started to notice leg problems, these were traced to bone spurs in neck vertebrae, probably caused by the ejection.  Surgery fixed the problem.
(Collins goes into this and many other details in his biography by the way.)

For those who do not recognize the name: Michael Collins flew again.

yes that's right, after having the surgery the problem was (almost completely) fixed and his next spaceflight was... the big one to the moon!


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Why is Hydrazine used to power the F-16's EPU?
Why does the military use hydrazine to power the F-16's Emergency Power Unit (EPU)? What is so unique about Hydrazine fuel that it's  needed to power the EPU? Why not use a less volatile and less hazardous fuel?

Hydrazine is used so that if one is stranded on Mars, you have a single source for power, water, and oxygen!   ;)

The EPU of F-16 is fueled with a monopropellant hydrazine mixture, H-70, which contains 70% hydrazine ($N_{2}H_{4}$) and 30% water, by weight.
The main requirements for the EPU are that it should be simple, maintenance free, supply power immediately and consistently for the required time. Use of Hydrazine assures this while requiring careful handling.
Basically, the catalytic decomposition of hydrazine produces ammonia, nitrogen and hydrogen. Exhuast Gases from EPU Turbine contain 40% Ammonia, 17% Nitrogen, 15% Hydrogen and 28% Water.
$3N_{2}H_{4} \rightarrow 4NH_{3} + N_{2}$
$4NH_{3} \rightarrow 2N_{2} + 6H_{2}$
$3N_{2}H_{4} \rightarrow 4(1-x)NH_{3} + 6xH_{2} + (2x+1) N_{2}$
where x is the fraction of the $NH_{3}$ disassociated.
The water modifies the decomposition temperature (the EPU reaches temperatures of ~870 $^{\circ}C$), preventing thermal damage to the catalyst bed and the turbine parts. As the water removes heat, it is turned into steam which aids in powering the EPU.
The EPU, using hydrazine spins up to approximately 75,000 rpm in 2-3 seconds (The F-16 EPU starts within 2 sec.). It would take a much greater time if another fuel, like JP-8 were used. When required (EPU runs normally on engine bleed air), hydrazine is forced into decomposition chamber by nitrogen pressure, where the above reactions produce the gases to run the turbine/gearbox. The decomposition of hydrazine produces enough pressure, eliminating the need for a compressor, thus saving weight and also eliminating the need for an igniter, reducing complexity.
For the given weight, it provides continuous operation for the required time. In F-16, the EPU carries ~25l of hydrazine, which permits operation for about 10 minutes under normal load conditions and 15 minutes if the loads are less (i.e. in ground). If any other form, (like battery or cartridge) were used, it would be difficult to have a long operational time without heavy increase in mass.
For a combat aircraft, RAT is not an option. Also, a hydrazine powered EPU would work in any altitude or during maneuvering as it does not need an external oxidizer supply.
References:
Exhaust Gas Composition of the F-16 Emergency Power Unit by Harry J. Suggs et al.
Technical Order 00-105E-9, USAF
AFR 110-14 USAF Aircraft Accident Investigation Report.
F-16 manual
Thanks to @Peter for pointing out errors.

And why is a RAT not an option for combat aircraft?  They’re used all the time in this role.

To fill the voids in aeroalias' answer:
Hydrazine is a monopropellant, something which does not need to be mixed and burned to free up the energy contained in its chemical bonds. This energy is freed by letting the hydrazine stream over a catalyst, in case of the F-16 EPU that is iridium. This breaks the chemical bond, producing ammonia, nitrogen gas, hydrogen gas and heat which converts the water into steam. Heating increases the volume of the gasses and the steam so they pick up speed, just like the gasses in the combustion chamber of a jet engine. In the catalyst chamber of the F-16's EPU the temperature reaches more than 800°C in just a couple of milliseconds, and no combustion is involved! This high-pressure, high-speed gas flows through a small turbine which in turn drives a generator and supplies hydraulic pressure.
Compression is not needed because pressure is supplied from the bottle containing the hydrazine-water mixture. Using a monopropellant also avoids any ignition problems and makes the setup very simple. Since hydrazine is quite stable at high pressure and ambient temperature, the shelf life of a hydrazine engine is high, and the liquid state of the hydrazine-water mixture makes its storage very compact. Just what you need in a fighter aircraft.

Are special measure taken to keep the failure probabilities very low under normal operations low? e.g. some failure modes I can think of (A) Leaks of toxic hydrazine during ground ops & maintenance (B) Combat damage to Hydrazine tank (C) Accidental release during flight (D) Detonation stimulated by external fire

Are special decontamination procedures needed in case of F16 crashes? Or even after an aircraft that has needed EPU deployment returns to base? The lethal dose of Hydrazine I recall is in ppm quantities?

@curious_cat: Related: Exhaust gas composition of the F-16 Emergency
Power Unit, see page 12 and F-16 Aircraft Hydrazine Procedures.

@curious_cat I think you've misrememberd. Wikipedia says that the limit for hydrazine traces in pharmaceuticals is in the low ppm range, which suggests that the lethal dose must be much higher.

@curious_cat Technically anything that has a lethal concentration could be said to have a lethal dose in ppm. For example, it could be 0.000001 ppm or 900,000 ppm. Or 2,000,000 ppm. :)

@DavidRicherby Perhaps the amounts in pharmaceuticals are measured in ppm relative to the mass of the pharmaceutical (whereas LD50 is measured relative to test subject body mass?)

@reirab Yes, limits for contamination expressed in ppm would be relative to the mass of the product being considered. A figure quoted as ppm is very unlikely to be an LD50, since LD50s are pretty much always measured in milligrams (or similar) of substance per kilogram of body weight. That's the same thing as parts per million, of course, but it seems to be very rare for it to be expressed that way.

@DavidRicherby Yeah, it's an unusual way to express it, but I assumed LD50 when talking about a "lethal dose," as a "lethal dose" relative to the mass of the substance wouldn't make any sense (i.e. ingesting 500 femtograms of something dissolved in a nanogram of water is not equally likely to kill you as ingesting 500 milligrams of said substance dissolved in a kilogram of water.)

LD50 for mice seems to be in the 10 to 30 mg/kg range. I found an interesting story of a sailor who accidentally drank dilute hydrazine and survived, after 2 weeks treatment (http://www.toxipedia.org/display/toxipedia/Hydrazine).

@reirab Well, I typically see it used in the sense of 1 ppm or 10 ppm or 150 ppm or even 500 ppm but something that reaches the next higher common unit of measure is not.

On a related note... here's an F-16 landing with EPU running, and it's commented about on the radio:  https://www.youtube.com/watch?v=A0DdpC7GV3A

All the pluses noted in this answer begs the question, "Why isn't hydrazine used to power APUs in all aircraft?"

@FreeMan Hydrazine is nasty stuff. It needs discipline to be handled, and it is good for only a short running time. A regular RAT runs as long as the airplane is moving.

That makes sense, @PeterKämpf, and saves me typing up a new question. Thanks.

Hydrazine use is related to aircraft stability. Without power to the computers, the F-16's preferred flight attitude is flying tail first. The basic aircraft design is aerodynamically unstable, intentionally, to achieve high performance. The flight control computers maintain stability.
If electrical power goes down, the pilot suddenly needs wading boots. To prevent such unfortunate circumstances, the APU was specified to be on-line at full power 0.25 seconds after power failure.
Apparently, in the late 60's to early 70's (design years) nothing else could meet the rapid start, weight, and power endurance requirements.


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Would it be viable to install a screen in front of jet intakes to prevent them from sucking in birds?
Why isn't there a protective screen with large diameter holes (approx 2') mounted in front of the jet engine intake to protect the turbine blades? This would  keep larger birds and large ground debris from getting sucked in, which can cause serious internal engine damage.

Would the filter really prevent the birds to go inside the engine, considering the energy of the impact?

What sort of screen are you imagining? It's hard to save a bird when the relative velocity is 300 mph.

@raptortech97 I think the goal is to protect the engine from the bird, not protect the bird from being hit by something at hundreds of miles per hour.

If you did have a screen, what's going to happen when the bird hits it?  The suction from the engine isn't going away, since you don't want to shut the engine down in flight.  Either the bird will get sucked through the screen in pieces and go into the engine anyway, or it will get stuck on the screen and disrupt the flow of air, which seems like it might be a problem.

@DavidRicherby you're right, I misread the question

@NateEldredge: A 5% drop in performance, and a cheap repair both seem like real benefits. Many safety measures (e.g. airbags) aren't so much about preventing accidents but more about damage reduction.

One also has to wonder whether the mesh can actually save an engine. It obviously cannot keep the bird out of the engine; all it can do is slice it up a bit before it hits the blades.

You really only need to protect the engine core, which is more practical than protecting the whole fan.

mig-29 actually has a intake screen

Modern high-bypass turbofan engines work by pulling in immense volumes of air and accelerating it.  A screen as proposed would make that task far more difficult, which would ruin the efficiency of the engine.  It's also pretty well unnecessary.
Jets worldwide take plenty of birdstrikes every day.  Unless the pilots see it (hitting the windscreen will do that) or hear it (hitting something near the cockpit) or the bird goes into the engine core (which causes the smell of burned bird in the air conditioning), the chance that the crew knows about it before the next walk-around inspection is pretty slight.  The vast majority of birdstrikes are utterly inconsequential.  (Except for the bird -- ruins his day pretty thoroughly!)
Yes, there are a small number of very highly visible events where birds do disable an aircraft -- the "miracle on the Hudson" and the loss of an AWACS in Alaska come to mind, and there are others.  And it's possible for a birdstrike on an engine to cause significant damage IF the bird is large enough AND it goes into the core, but in the big picture, that is actually pretty uncommon.
Thus, the aircraft manufacturers and operators end up accepting the risk of a catastrophic birdstrike, because the alternative of protecting the engine as suggested is too expensive when the effects on the efficiency of the engine are considered.
One other point, bird flesh is pretty easy for an engine to chop up and digest.  If a big bird hits a metal shield at high speed, there would be the risk that the shield could be damaged enough that some of the metal would break apart and go into the engine as well, and THAT would cause far more damage than just the bird.
Fun video of stuff being shot into an engine during testing

well said and great videos

I think it's worth mentioning that decreasing the efficiency of the engines is itself a safety risk.  Less power for hot days, short runways, collision avoidance maneuvers, etc.

more important I think is that it wouldn't really do much good. The screen would just turn the bird into chunks of bird. While that might prevent a bent fan blade at the first low pressure fan, maybe, it wouldn't do much more.

So we notice the bird if we see it, hear it, or smell it.  Hopefully there's not to many documented cases of a flight crew noticing the bird via taste or touch!

A few Russian/Soviet fighters had retractable FOD screens on their engine intakes (MiG-29 and Su-27 IIRC). The assumption was that they would operate from damaged runways or roads and the engines would need protection against Foreign Object Damage (FOD).

Right air intake of a MiG-29 with main doors closed and louvres on the wing root opened.

Mind that these were not intended for operation in flight. They are only operated during takeoff and landing, they restrict the airflow too much to be practical during regular operations (the performance of the aircraft suffers too much) or even when taking off at high weight.

Nor are they designed to take a bird at cruise speed.

Do you encounter many birds at cruise ? I thought they were mainly a danger during take off and landing. You don't do much bird spotting at 40,000ft

Depends on your mission profile. The MiG-29 was designed primarily as an air-superiority fighter (originally the answer to the F-15, itself developed in direct response to the MiG-25), but was adapted to multirole use especially with the M variant; air-to-ground mission profiles even for deep strikes often involve relatively low-altitude cruising.

@KeithS - I meant for commercial airliners - bird strikes are only an issue at take-off/landing. Not that FOD screens are practical - but they don't have to work at mach 0.95

@NobodySpecial that would depend on your routing. Flights are rerouted during bird migration season to avoid high altitude flocks for a reason. There are birds that high up, just not many.

Screening the primary intake like this works on a jet fighter where the engine is buried in the wing/fuselage and the wing top can be used as an alternate air intake. For a "standard" configuration airliner, @NobodySpecial, with engines hung below and forward of the wings, what would be the the possible alternate air intake path?

Screens were actually used on the first prototypes of the Me-262, but soon abandoned when they were found to be more of a burden than a help.
If you look carefully at the picture of the Me-262 V3 below, you can see the spherical screens on both engine intakes.

Today, screens are used only in ground tests. See the picture below for the Rolls-Royce version:

The big surface of the sphere reduces aerodynamic losses, which are small under static conditions anyway, but this contraption would obviously be totally impractical in flight.

It's probably also worth noting that, while the big surface of the sphere reduces aerodynamic loss in the case of a test fixture that is stationary with respect to the air around it, it would cause an incredible amount of drag were it actually moving through the air.

The screen in the second picture isn't really to block FOD, but it does have that added benefit.

Doesn't that show the danger of ingesting bubble gum  while running in reverse?

There are three problems with this idea:
(1) To make a screen strong enough to withstand the body of a 15-to-20 pound bird hitting it at 500 miles per hour, would require thick wire which would significantly block air flow.
(2) Such a screen would be very liable to collect ice, so it would have to be heated to high temperature. This would be expensive and would increase the maintenance burden for the aircraft.
(3) If part of the screen failed and broke off for any reason and went into the rotors, it would destroy the engine.

When flying any surface that is exposed to the air will generate drag. That screening, although full of holes, will create significant drag when exposed to the air that is entering in the airplane.
Also, it will distort the air entering the engine reducing the efficiency of the engine and increasing fuel comsuption.
Globally, the extra drag and the higher fuel consumption is more costly than the increase of weight needed for generating extra protection on the engine nacelle.


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What are the visual differences between the F/A-18 Hornet/Super Hornet and the EA-18G Growler?
I was looking at the Northrop Grumman website and came across the EA-18G Growler, which looks very similar to the F/A-18. What are the visual differences between the two?

These are two very different airplanes with different missions, your question is unclear.

EA-18 Growler Wikipedia | F-18 Super Hornet Wikipedia

Super Hornet is a "larger" version of the Hornet. The growler has 90% of the same components as the superhornet.

One big difference between the Rhino and the Growler is the wingtips.  Looking at the Growler's reminds me of training wheels on a Ducati...

On this image there are few external differences. Mainly the canopy, but from @RonBeyer links, I see they can be both two seats.

@GdD:  "These are two very different airplanes with different missions, your question is unclear." No, the B-52 and the F-16 are very different airplanes. The F/A-18 and EF-18 share a common airframe, and some mission overlap.  And the question is perfectly clear...

You asked about visual differences. The main visual difference is that there are no guns on the EA-18G, just AIM-120 AMRAAM or AGM-88 HARM missiles. Other than that the visual differences are minimal. The airframe is still a F/A-18F Super Hornet, where -F stands for twin-seat. Engines are also the same General Electric F414-GE-400, however I suspect there could be some differences in regards to the engine auxiliary equipment, such as the electrical generator. I also suspect there is additional equipment added for the sole purpose of conditioning the electrical power and insulating everything to keep interference minimal. It is even possible that there are optical fibers in areas where on the F/A-18F copper cables are still used.
Main differences:

Dedicated electronic attack equipment, e.g. what makes the aircraft an EA-18G, has been put in the place of the cannon.
The EA-18G has one extra protruding antenna on the back, along with the satcom antenna behind it.
The missile launch rails on the ends of the wings seem to be permanently modified to support the ALQ-218 Tactical Jamming Receiver, which is the same pod as on the EA-6B Prowler.

Here is an image of the EA-Growler showing some of the external modifications and what they’re for:

Source: airforce.gov.au/Archive.org

Archive.org to the rescue.

Physically, an EA-18G is a EW derivative of the F/A-18F Super Hornet multirole fighter.  This was a cost effective means for the Navy to develop a replacement for the EA-6B Prowler aircraft for the fleet SEAD/DEAD role.  The most obvious physical differences between the Growler and the Rhino are the replacement of the missile rails on the wingtips with the ALQ-218 electronics pods as well an additional external antenna.  The M-61 gun has been removed on the EA-18 and replaced with an electronics pallette.  Loaded out Growlers will usually sport 2 or more ALQ-99 jamming pods on the wing and centerline ordnance stations, easily recognized by their oblong shapes and front mounted RAT power generator.


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Why would the USAF have no support for autolanding?
One thing I noticed when reading through the KC-10 flight manual (see page 184 for the specific reference) is that the KC-10 lacks support for Category III operations, unlike its civil DC-10 brethren.  What was the purpose behind the USAF asking MDC to remove capability from a military airplane?
Furthermore, military ILS systems in the US are qualified to CAT II at best, even in areas where air carrier airports are well-qualified for CAT IIIb minima.  For instance, Joint Base Lewis-McChord only has a CAT II approach to RWY 34 whereas nearby Seattle-Tacoma Int'l has CAT IIIb approaches to 300' RVR on all three of its primary instrument runways.  Considering that I seriously doubt the USAF would somehow be buying ILS equipment inferior to what's available in the civil market -- is there some other reason they don't provide any low-visibility capability better than the CAT II minima of 100' DH and 1/4 mile visibility, as the published PAR minima in the A/FD are no better, either?
Update: KADW RWY 19R has a CAT IIIa approach, good to 700' RVR.  This seems to be the only military CAT III procedure published, though.  Perhaps the VIP airlift aircraft (E4, etal) have autoland support, even though the normal military heavies don't?

Well, where's the fun in letting the plane do all the interesting bits of flying? :) real Air Force jocks spend 80% of their flight hours inverted, including short final.

@JonStory Hopefully they're not flying inverted short finals in the KC-10s, though. - haha

Only empty ones

@reirab I bet any aircraft could do it once

@KorvinStarmast -- then why are the published PAR minima in the A/FD no better than CAT II?  Not enough practice?  Or is PAR below those minima basically a military-specific (i.e. unpublished/not for civil use) procedure?  (As far as budget goes, I'm not sure if the DC-10s autoland was an airline-option (i.e. extra cost to add) thing, or something that was part of the base DC-10, and if the latter, how much removing it cost vs. having it available for use on the KC-10)

Unrecognized - Check the DoD FLIP pubs for PAR mins.

@KorvinStarmast -- if I could get my grubby civvie paws on a copy, I would ;) (no, seriously -- it seems the FLIP AP/1 has way more stuff in it than the A/FD, but it's not exactly as available as the FAA pubs are)

The Super Hornet can't even shoot a VOR approach, much less an ILS. We are TACAN/ PAR only.  That's fine at the boat, because that's how we operate, but apparently the Navy still hasn't figured out that there are stationary airfields that don't float.  Maybe someday we'll upgrade and get the finest in 1980's technology.
In all seriousness I'm assuming it has to do with operational requirements and money.  The less the Navy spends on stuff like ILS equipment, the more they can spend on stuff that goes boom.  Also, if the weather is questionable at home we probably can't safely do our training mission anyway, and out at sea, we have some other systems that help us land on the boat in bad weather.  It would be really nice though to be able to use civilian fields as legal weather alternates.  It gets a little tricky sometimes when planning cross countries.

The KC-10 is Air Force not Navy, though.

@raptortech97, sure, but costs and operational requirements are factors that all branches of service must take into consideration.  Some branches just have more money to 'pump' into stuff like pools, but I'm not bitter.

I'm assuming they're going to have a bingo weather divert before launch that should satisfy those requirements, and in a real intercept, FAA takeoff minimums no longer apply.

That raises a question -- how would you recover fighters if CAT III conditions are present over a wide area and you had to scramble into such conditions?

Closest alligator to the boat man, you're gonna kill bodies first and then deal with that later.  If people punch and we lose assets then some instruction will probably be written to prevent it from happening again, but the likelyhood of that happening is pretty slim

"the Navy still hasn't figured out that there are stationary airfields that don't float" Right!

I was a Flight Test Engineer on DC-10-10 Ship 2 which was the Avionics Test airplane during initial certification. The DC-10 airplane was certified to CAT III Approach and Landing. The KC-10A was never tested nor certified for CAT III because the centerline Air Refueling Boom limited the flare of this model compared to the other DC-10s. And the Government chose not to fund the additional tests required to meet FAA requirements.

That is a very nice inside-knowledge answer. Welcome to aviation.stackexchange.com, @Gunn.

This seems to be as an authoritative answer as we could hope for. Maybe UFO will stop by and change the check mark.

NB: speculation, IANAP
Note the assault strip in the approach diagram for McChord Field.  This is a very short strip of moderately improved runway for simulating a combat landing on a short airfield.  Most (if not all) USAF pilots need to qualify regularly with such landings.
Unlike commercial aircraft, which take off and land almost exclusively at improved facilities, military aircraft should not expect ILS landings in their travels.  We've seen recently how over-reliance on automated technologies can have disastrous results, in most cases fatal.  Thus the military places the emphasis on training the pilot, and not in relying on their equipment not to fail.
So why put ILS systems at military airfields at all?  For one, many military airfields also serve as regional airports.  They might also give pilots proficiency in landing at commercial airfields.  It is also likely that they exist as a minimum for commercial pilots to use in the event of an emergency landing (for military-only runways).

Military aircraft (especially tanker-sized ones!) often use commercial airfields as intermediate waypoints, for one; for two -- close-to-manual landing technology for CAT III approaches has only come of age recently with the advent of commercial HUD systems.  It makes no sense that the Air Force would have to completely shut down operations while the air carrier airport next door is in (mostly) full swing still...

KC-10 aircraft are tankers, and do not require assault landings (those are primarily done by the workhorses of the AF, the C-17 and C-130)

@SSumner My understanding is that KC-10 aircraft are multi-role. While assault landing may be over stating it, the RAF (I know little about USAF) use(d) these kind of aircraft for troop deployments to Afghanistan and similar - requiring operationally specific procedures.

@Dan - they are "multi-role", but they have much more limited capabilities, especially in the term of short-field landings.

@Dan -- remember that the KC-10 is a DC-10-30F (really, something of a QC with the palletized seating) with pods and a boom (and no autoland)

Haha, well we certainly don't exclusively rely on our equipment to work, its constantly breaking.

Maybe they consider the expense as not being worth it.
With commercial airlines being on time and at the correct airport matters most; the military can "afford" to divert or delay if local conditions aren't favorable more easily. Hence, there's probably very little perceived need for sophisticated systems.

Fair point - it is a lot of maintenance work to keep an autopilot at Cat III tolerances, far more work than keeping it to regular certification standards. Plus the aircraft & crews have to maintain Cat III currency, which means having the Cat III ground equipment (redundant Loc + GS transmitters, plus ALSF II lighting) at all the bases. Big $$$ for a fairly rarely used capability.


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How does a coaxial rotor helicopter achieve yaw?
Without a tail rotor, how does a coaxial rotor helicopter achieve yaw control? Does a coax have to bank in order to turn?
The link goes to wikipedia's article, and down a ways it says:

Rotational maneuvering, yaw control, is accomplished by increasing the collective pitch of one rotor and decreasing the collective pitch on the other. This causes a controlled dissymmetry of torque.

However, I cannot understand what it's saying. AFAIK both rotors always spin at the same RPM because the mechanical engine links are built that way and it's set in stone (correct me if I'm wrong). So I can't see how one rotor makes more torque.
EDIT: related, is this kind of yaw, however it's achieved, slower or faster than yawing in a conventional tail helicopter?

Your quotation doesn't say the RPM differs; it says the blade angle differs, so 1 rotor works harder than the other, which causes the desired yaw.

I would say it is unlikely that the two rotors are mechanically coupled, since any torque difference would by transmitted through the drive train. I think it is far more likely you simply have two engines. (take this with several grains of salt).

@Asad They might not be mechanically coupled, I don't know. But I'm pretty sure both spin at approximately the same RPM because that's just how all single rotor heli engines work (as far as I know). If they're not coupled, a coax could just have 2 engines like you said. However, there's a thing called a free movement clutch or something like that, that allows a gear somewhere to decouple if one axis speeds over the other. So it may be possible that they are coupled after all.

In addition to @Airsick's excellent answer, some coaxial helicopters, like the Gyrodyne Rotorcycle, use tip brakes to achieve yaw authority.
Below are a couple examples of tip brakes, found at this website

A tip brake is a drag-inducing device on the end of the blade, that can be extended or retracted to increase or decrease drag.  To yaw in one direction, the tip brakes would be extended on one set of blades, but not the other, generating a net torque due to increased drag in that rotor.

With a bit of delay: tip brakes are indeed used to achieve yaw authority but mainly, if not only, in autorotation. This is due to the fact that in autorotation differential torque is very limited or even reversed, as well explained for example here.

When you increase the collective pitch of a rotor blade, it produces torque thus inducing a yaw in the opposite direction of the aircraft.  By the same token, reducing the collective pitch reduces the amount of torque it had been inducing.  This is evident in a single rotor helicopter with its need for an anti-torque rotor.
So in a coaxial rotor system, with the two main rotor blades counter rotating, increasing the collective pitch of the top rotors (thus increasing its torque effect on the main rotor shaft) AND reducing the collective pitch of the bottom rotors (thus decreasing its torque effect on the main rotor shaft) will make the aircraft yaw in the opposite direction that the top rotors are rotating.
So let's say that as viewed from the top of a coaxial helicopter, the top rotors rotate clockwise and the bottom rotors rotate counter-clockwise.  When left pedal is applied (to point the helicopter's nose to the left or yaw counter-clockwise) the collective pitch for the top rotors is increased (increasing the torque counter-clockwise) while the opposite is done to the lower rotors (thus decreasing the clockwise torque).  I hope this helps!

Good first answer, welcome to SE Aviation.

In simple terms, you increase the drag on the rotors going one way, and reduce it on the rotors going the other way.
Normally you increase the pitch of one rotor (meaning more lift and more drag), and decrease it on the other (meaning less lift and less drag). The lift balances out, but the difference in drag causes yaw.


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What is a heat dissipater and how does it work?
Wikipedia's Mi-24 Hind article (a Soviet helictoper) says:

Heat dissipaters were also fitted to exhausts to decrease the Mi-24's heat signature.

There's no citation. What exactly is a heat dissipater and how does it work?

The heat dissipaters  are used to reduce the infra-red signature of the helicopter engine exhaust. They are also used in other helicopters, like the 'black hole ocarina' (BHO) infra-red suppression device used in AH-64 Apache.

Source: b-domke.de
The main purpose of the IR suppressors in use today is twofold:

Reduce the IR signature by reducing the exhaust temperature
'Shield' the hot engine from view.

The infra-red suppression systems in service today usually work by

'Bending' the exhaust, usually upwards, and shielding the exhaust from view by an insulating cowl. In these IR suppressors in Mi- 35 (export version of Mi-24), the exhaust is turned almost 90°.

Source: mamboccv.com

Mixing the hot engine exhausts with the cool air, effectively reducing the exhaust temperature. In the Black Hole IR suppression system, the exhaust temperature is reduced from ~600 °C to ~300 °C .
The RAH-66 Comanche had the infra-red suppression system integrated into the airframe (the exhaust was routed through the tail boom), though the principle is the same- mixing of engine exhaust with ambient cool air.

Source: sikorskyarchives.com

In some cases, the special high emissivity coatings are applied to the engine exhausts for reducing the IR signature.

Most of the present IR suppressors focus on achieving a thorough mix of the cool ambient air and the exhaust to reduce temperature and uneven mixing, in order to prevent 'hot spots'. Cooling of the exhaust pipe itself is achieved in some cases by using film cooling. In most helicopters, the infra red suppression system (IRSS) is optional and can be added separately.
The figure shows the schematic of the infrared suppression system used in AH- 64 Apache and the associated reduction in IR signature.

Image from Progress in helicopter infrared signature suppression by Jingzhou Zhang et al., Chinese Journal of Aeronautics, Volume 27, Issue 2


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Participating with "flight following"
What is the proper procedure for participating with "flight following" when leaving a non-control towered airport?

You can request Flight Following at anytime.
Personally, I wouldn't be in a hurry to request it as soon as you depart. Wait until you're established on course, in a cruise-attitude (instead of a climb), and everything is settled and running smoothly. Then know your position, and how you're going to report it. Know where you're going (both by name and ICAO identifier), and try to anticipate any questions they might ask.
Look for the Center/Approach/Depature where you are (look in your chart supplement for an airport close to you), and call up with:
You: "Seattle Center; November 12345: VFR, with request"
translation: Calling Seattle Center, this is N12345. I'm VFR (so you haven't heard from me before... don't be surprised!), and I have a request.
Center: "November 12345: Say request."
You: "November 12345 is SkyHawk, 10 mi. South of Harvey Field, 4,500 feet. Request VFR Flight Following to Friday Harbor"
translation: I'm a Cessna Skyhawk, my location and altitude will help you find me. I'm asking for FF to this other airport."
Center: "N345: Squawk 4532 and Ident."
You: (Set your transponder to 4532, press the Identify Button), and say "4532 and Ident, N345"
Center: "N345: Radar Contact, 11 mi. south of Sierra Four Tree, at 4,500. Traffic at your 1o'clock, 5 mi. North Bound, Altitude indicates 3,000."translation: I found you on my radar scope, and am describing the position I see you. (If you disagree, speak up!). You have traffic ahead and slightly to your right. Their transponder indicates 3,000 feet, but I cannot independently verify that.

You may not always have the luxury to wait.  For instance, in skyvector.com, plan a trip from 6B6 to PYM.  Eastbound, so VFR you'd want to be at 3500 once clear of the departure airport - but the Boston Class B is right there overhead.  In this case, I would contact Boston Approach as soon as I could, both to be aware of Boston-Logan traffic and to get cleared into the Class Bravo airspace at a legit altitude, vs skirting along just under and dodging Hansom-Bedford traffic and Norwood traffic.   Without the Classs Bravo right there, things could be more relaxed.

In a case like that, (ADS near Dallas), I contacted Clearance Delivery while on the ground:  They set me up for FF before I even taxied.

@abelenky When you make your request, be sure to state the altitude you will be cruising at.

This answer is good for non-towered airports.  If you're at a towered airport, though, it's easier to request FF from Clearance Delivery (or Ground if no CD) before you even take off; once tower hands you off, all you have to do is check in with Departure/Center rather than trying to request it while climbing or en route.

Like when the Approach you were talking with says "Nxxxx, flight following terminated, squawk VFR"? And some times adds "Contact xxx Approach on xxx.x in so many miles" Then you contact the next Approach area when you get closer to them, or contact Center if the next Approach is too far away.
Example, I was flying from Binghamton, NY up towards Buffalo, NY. Binghamton dumped me not far out of the area, Buffalo was still quite a ways away. I called NY Center - they said contact Binghamton. Told them Binghamton had just dumped me - they had me standby, apparently talked to Binghamton, came back and said contact Binghamton, I did and Binghamton gave me flight following for quite a ways more.
Sometimes you have to climb higher for Center to see you. That may have changed with ADS-B. Haven't really gone anywhere since I had ADS-B installed on February.
Work on your IFR rating. When on an IFR flight plan, you never get dumped.
(I am rated, just not current at the moment, but I'm working on it.)
[Hmm, looks like I misread the question.  My answer is more appropriate to "What can I do when flight following is terminated leaving me with no ATC to talk to, and in the middle of no where?"


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How do solo fighter pilots sleep?
Tonight I watched Nova's "The Impossible Flight", a documentary film about the around the world Solar Impulse project where a solo pilot set the world's record for a 5 day non-stop flight from Japan to Hawaii with a ~35mph TAS! The documentary showed the pilot practicing 20min naps and said "this is a technique military fighter pilots are taught...". (It is supposed to keep them from going into a deep sleep)
Many commercial sleep questions have been answered on stack such as;
Is a pilot allowed to sleep during a flight?
How are emergencies handled during In-Seat Rest?
So this question pertains to military pilots.

Is this practice common among most nations?
How is a fighter pilot woke up?
Is there a alarm in the radio system?
Does an air or ground controller wake them?
Or perhaps the documentary was misleading and only sleep is allowed with two or more crews?

Generally, the only time fighter pilots are asked to remain airborne long enough where this is a factor are when ferrying aircraft across the ocean, (or for long distances over territory where there are no intermediate refueling bases.)  Generally this is always done in multi-aircraft flights or formations or two or more aircraft, so even in a single seat fighter, you are not completely alone.
Obviously, the average fighter cannot carry fuel sufficient to last that long, so (again, generally), when this happens they accompany a refueling aircraft  (or have pre-planned rendezvous with refueling aircraft every few hours). So there is no need to "wake up" - they remain awake the entire flight. They are flying manually in formation off the wing of the refueling aircraft, or one of the other aircraft in the flight. If the flight is long enough where alertness is an issue, or if the flight occurred during periods where the aircrew would normally have been asleep, we were sometimes issued Dexedrine tablets to take to help remain awake and alert.
In peacetime, we would never deliberately plan a flight where from start of pre--flight planning, until engine shutdown would exceed 12 hours. This rule of course could be violated in the case of wartime or national emergency, etc. etc.

I'm a former active duty F-15E driver and flew three 15+ hour flights to Saudi Arabia or to the mid-east in 2004+.  I now fly a F-22 with the Hawaii ANG.
No military pilot sleeps, unless they are E3, cargo, or tankers, etc that have 2+ crews like airlines (so planes like that the crew can sleep as they have shifts). But BUFF, B1 guys, or fighter, Growlers or any of the same fighter or bomber types nope NOBODY sleeps.
For us guys and gals in the F-15E or any 2-seater, we chat and monitor. A refueling KC10 always accompanies flights like this and we do multiple refuels and those really wake you up, especially at night. We also chat with our other flightmates, but its really just monitor instruments, mission details and keeping spatial awareness, no different than an airline pilot. Yes, it gets very boring at times.

My answer exactly.  You’re liable to have a rude awakening if you do!

The awakening mechanisms of the brain are very capable. For instance, in this experiment, there was a requirement to wake up 15 minutes after the light has been turned off, and it worked for many students. Hence it is possible to wake up periodically, in response to something happening, or any combination of these. Also, the brain is capable of surprises response that alerts about anything unusual happening (engine sounds wrong, new acceleration, bring warning light in the dark cockpit), and this works also while asleep.
Hence the brain is capable of basic checks (accelerations feel as usual, engine runs OK, no bright warning lights, wake up me in 10 minutes) also while sleeping. As long as the plane does not require constant input just to stay in the air, this may be sufficient for the short duration of the nap.
It is obviously risky to rely on this, the brain must be set somehow to respond in a wanted way, but I believe that first aviators long time ago used this capability to cover long distances alone.

this may be interesting but it doesn't answer the question.

I think it does - they can have a short nap because the brain is capable of basic checks (accelerations feel as usual, engine runs OK, no bright warning lights, wake up me in 10 minutes) also while sleeping. As long as the plane does not require constant input just to stay in the air, this may be sufficient.

The question asks whether fighter pilots sleep on long flights and if they do what mechanisms are there to wake them up. I cannot see how this applies, perhaps some refinement would help make it more applicable.

This answer says that a brief sleep is theoretically possible, but not that it actually occurs (at least deliberately). I'm skeptical myself, and would like to see references that indicates pilots doing this deliberately.

Ferrying aircraft from North America to Europe is similar, and with legs of 18 hours, flying lower, in the weather, it was at times a physical challenge.  Add to that the discomfort of wearing an immersion suit, and it created a situation where I at times wondered if flying should be so little fun.
I can't speak of round the world flights, but a ferry flight might have a "duty day" of 24 hours, which is quite manageable. A steady diet of that might not be, but once a week or so it is tolerated.
The excitement of performing the navigation (pre-GPS days), managing the weather with few resources, and worry about either splashing in the drink or having a leak in the waterbed like bladder inside the plane tended to counter any drowsiness. If higher, hitting the O2 can also be helpful. It certainly brings out the stars over the ocean.
It is noteworthy that, more so in the past than recently, many medical residents would work similar duty days. Rather than just managing a flight, they might be doing procedures where a caffeine twitch could have adverse effects, and need manual dexterity and cognitive alertness.
Also, in the case of U-2 pilots, recent typical flights, providing combat support average in the 12 hour range.  It used to be that typical mission times were about 8 hours.  That is a long time to be confined in a moon suit.
So from the standpoint of most deployments, in the context of single pilot fighter oceanic flights, I would say that the demands of the occasional pond crossing is manageable.


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Clearance limit of VFR practice IFR approach?

When a VFR aircraft has been approved by atc to perform a practice approach, is the aircraft also cleared for a published missed approach procedure?

Rolling back my edits is completely fine - it's your question - but I suggest you leave the FAA tag there if that's the jurisdiction that you're interested in. It's much easier to answer questions about procedures (and regulations) if we know which country it is.

I agree with @Pondlife. Please provide the jurisdiction you want answers for, as this may vary.

I was always asked, "How do you want to terminate the approach?". I can't think of a time I was not asked. After that, they give the long winded speech about remaining in VFR and separation is not provided.

Related: https://aviation.stackexchange.com/q/88954/

I'm assuming you're asking about the US, in which case the answer is no. The AIM 4-3-1(e) says:

VFR aircraft practicing instrument approaches are not automatically
  authorized to execute the missed approach procedure. This
  authorization must be specifically requested by the pilot and approved
  by the controller. Separation will not be provided unless the missed
  approach has been approved by ATC.

If one asks for it.  When I was working on my instrument rating, we would often request a practice IFR approach using one of the various methods (ILS, Localizer, VOR, GPS, PAR, etc.) with 'the option' - actually land, or fly the Missed approach. Then the instructor could mix it up so you wouldn't get in the mindset that every approach would be successful. You might be too off course, too high, too low too early, or he could say you were still in the clouds at the point where you had to decide to continue descending. Sometimes we'd be cleared for the Miss as shown on the approach plate, other times we'd be given an alternate route to fly, perhaps to make way for a plane that would have conflicted: landing on intersecting runway, or taking off and climbing towards us; sometimes we'd practice the same approach from the same end a few times and basically just fly a closed pattern vs doing the whole climb out and procedure turn or hold, sometimes we'd do the approach from one end, then fly out and do the approach from the other end (say like ILS from one end and GPS from the other).  ATC at the smaller airports are generally friendly to work, and as long as you're flexible to accomodate planes that are actually landing, or departing, they have no problem working with you.

Terminology is important here.  You asked whether if under VFR, you were "cleared" to execute a missed approach.  There are two points worth mentioning:
1.)  Under VFR you are not actually cleared under the IFR definition of this term.  Your other wording was more correct, you are "approved" to execute the instrument procedure for practice under a different set of rules.  To put it in different terms, under VFR you have no clearance limit because you have no clearance.
2.)  When you are IFR you are not technically cleared for the missed approach procedure either in accordance with the standard definition of the term.  (I will likely get some comments on this, but let me explain what I mean...)  Your IFR clearance includes your route of flight and altitudes up to and including your clearance limit.  Typically your intended point of landing is the termination of your flight, or your clearance limit.
The missed approach airspace will be protected for you under IFR, and you will have separation when and if you execute the procedure, but you are technically not cleared for anything beyond your clearance limit.  That's why execution of a missed approach is an immediate mandatory radio call.
Think of the missed approach like an emergency procedure, because that is almost what it is.  And it is why they generally end in holding pattern so that you and ATC can sort out further clearance to your alternate.
In training and practice things are a bit different, but the important thing is clear communication of intent and understanding what ATC expects, or has cleared you to do.  (i.e. the "option" gives you wide latitude...)

@StephenS, you would probably know better than me, but I was always taught that "cleared" was specific to IFR.   (specifically as it relates to a destination or approach procedure, T/O and Ldg clearance excepted...)  In other words, if you are cleared for an approach and the weather drops below VFR, you are still cleared for the approach.  Otherwise how does your TRACON distinguish between IFR and VFR?

@StephenS, let's make sure we are on the same page here:  If you request an instrument approach, and they clear you for the approach, you are now IFR! Otherwise how would you know that the controller intended "cleared" to mean that they knew you were doing it under VFR?  They have no idea what your rating is, or whether you have a safety pilot or not.  Cleared for an approach means you are now operating under IFR unless the controller includes specific verbiage acknowledging that you are to remain under VFR.  I mention this in case your assertion is based on a misunderstanding.

I'd be interested in a controller's perspective on this practice...

@StephenS (and MH): Practice at my facility is to issue a "Maintain VFR" when giving the initial vector toward the downwind (in accordance with the .65 4–8–11a5) and then when giving the PTAC to issue "maintain VFR" instead of "Maintain 3000". So: "N345, five miles from FIXXX, turn right heading 180, maintain VFR, cleared ILS runway 20 approach." We do provide modified IFR separation from other traffic but this is NOT an IFR clearance and the pilot may NOT fly into clouds even if their instruments are telling them to.

To be very clear: 1) we do issue an approach clearance (using the word "cleared") to VFR aircraft; 2) this is not an IFR clearance, but we do provide modified IFR separation; 3) we do not provide modified IFR separation in the missed approach unless specifically requested and approved. See all of 4–8–11 for more info.

But some facilities may give a hard altitude during the PTAC, and I don't think that's explicitly illegal. In any case it does not make you IFR and does not relieve you of your cloud clearance rules. The only way to make someone IFR is to say "CLEARED TO [clearance limit]," which is not what's happening here.

"Practice approach approved, no separation services provided" means you are not getting the modified IFR separation (by the way that means 3NM/500' instead of 3NM/1000'). Which one you get depends on whether the facility has published a Letter to Airmen saying you'll get mIFR sep at certain airports. Neither option is an IFR clearance.

@MichaelHall I’ve deleted my previous comments since randomhead has thoroughly addressed the topic here: https://aviation.stackexchange.com/q/88954/


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Why didn't the U-2 spyplane have any chaff?
The U-2 spyplane was shot down over Russia in 1960 and over Cuba in 1962, both times by a radar-tracking missile. Why wasn't it equipped with any chaff to throw off the missile?
Chaff is just a cloud of aluminum particles that return a big radar blur, masking the real craft so it can get away. The missile would home in on the chaff instead since it's a big juicy radar target. Chaff can be stored in very small cylinders near the tail of the plane, and the radar lock warning would let the pilot use it at the right time.
Chaff was invented in World War 2, giving plenty of time all the way to the sixties. So why wasn't this airplane equipped with chaff?

Chaff only works if you know the radar frequency. There was no knowledge on Russian missile radars at this time, so any chaff would had needed a mixture of different lengths, burdening the aircraft with extra weight. On a long range mission it is easy to expend all chaff quickly and be hit later anyways.

In the original U-2, space was at an absolute premium as well, so finding a place to put a chaff dispenser would have been difficult.

There are two main reasons for this:

USAF and CIA believed that the Russians (or anyone else) wouldn't be able to shoot down aircraft operating at (>60000ft).
Most of the aircraft operating during that time did not have chaff dispensers to deploy chaff as needed. For that to work, the pilot has to either visually acquire the missile or have a RWR, which became widely used only in the later stages of Vietnam War.

Another important reason is tactics. The chaff was not used in WWII in a tactical capacity i.e. to protect individual fighters, but to provide blanket coverage to bomber fleets. This practice continued well into the Vietnam War. For example, specialized aircraft (usually fighters) will dump chaff to provide a 'corridor' for following bombers. For an aircraft on reconnaissance mission, this is as good as advertising its presence.
A lot of aircraft in that era went without any countermeasures. For example, the English Electric Lightning carried no chaffs till its retirement in 80's.

At the time, it was believed that no missile could hit the U2 at 70,000 feet although this was more a belief driven by overconfidence and arrogance.  When the U2 was designed this was true and there was simply no need to fit countermeasures.
Following this incident, flights over Russia were stopped.
Flights over Cuba were made in the belief that there were no SAMs and of course, it was a U2 that captured the photographs which showed the Soviet deployments there.  Overflights were then stepped up to gather as much intelligence as possible whilst accepting the risk of being intercepted.

overconfidence and arrogance I think that's a bit uncharitable. Speed and/or altitude were very effective defenses at the time (still are, to an extent)---indeed that's how we initially expected to keep our B-52s safe. The U-2 successfully operated hundreds of miles inside Soviet territory for years before Powers was shot down, despite being tracked and pursued a number of times (Power himself was captured 1300 miles inside Soviet borders). Being shot down or captured was always a risk; Powers himself carried a suicide pill just in case. But the US felt the risk worthwhile.

In sum, there were a lot of reasons to be confident (which isn't to say there weren't indications that the U-2 was more vulnerable than was thought), but no one thought the U-2 was truly invulnerable---which is the major reason Eisenhower himself individually approved each overflight of Soviet territory---he feared the U-2 might be shot down and the pilot captured. And let's not forget the pressing need for good intel inside Soviet borders. Earth observation satellites did not yet exist, so a lot of the intel the U-2 acquired could not be obtained any other way.

Flights over Cuba were made in the belief that there were no SAMs - No, the US was WELL aware of Cuban-based SAMs---in fact, that's why the US limited U-2 overflights for five weeks before the Cuban Missile Crisis, fearing another shootdown. When overflights restarted, they just didn't expect the Soviets to actually shoot at the U-2s. They were half-right; Soviet commanders were ordered not to shoot, but an individual commander disobeyed and actually took down a U-2.